In the application of surface treatments to bottles and jars, where it is desired to coat the containers while they are hot from the forming of the glass, it is customary to use organic metallic compounds, such as stannic chloride and stannous fluoride in vapor form. Titanium compounds, such as titanium tetrachloride or tetra-isopropyl titanate, likewise have been found to be particularly useful in producing a titanium dioxide coating on the glass bottles. The oxide coating is very thin, usually in the range of 40-120 microns in thickness.
Methods and apparatus used to generate and propel the vapors into contact with the hot bottles to be treated have been the subject of several patents, such as U.S. Pat. No. 3,323,889 to Carl and Stiegleman and U.S. Pat. No. 3,561,940 to Scholes.
These apparati generally consist of a hood positioned over the machine conveyor for transporting the ware in single file from the forming machine. The treatment vapors are fed to the hood, which typically is in two sections facing each other on opposite sides of the conveyor. The tin or titanium vapors are propelled from each side to contact the two sides of the moving ware. In order to conserve the metallic compounds, it is customary to recirculate the vapor from one side of the hood to the other, adding new vapor only as it becomes depleted.
As indicated above, the hoods are fundamentally designed to propel the heated metal halide vapors across the conveyor carrying the hot container to be treated. In order to prevent the hydrolysis of the vapors on the bottles, it has been found necessary that the vapors be heated to a temperature above the dew point for the particular treatment material. Thus, provision is made to heat the vapor itself prior to its being conveyed or blown across the conveyor. This typically is done either by a heated source of compressed air in which the vapors become entrained or by heating the vapor after its production and prior to its being conveyed in contact with the side wall of the container. Obviously, moving the container into a position in front of a moving stream of heated metallic halide vapors would only effectively treat that surface which is in the line-of-sight of the vapor generator and, while it could be possible to rotate the container and thus provide 360.degree. or total circumferential coating of the container, it has been found more economical and easier to provide two streams of vapor issuing from opposite sides of a moving conveyor to impinge the two sides of the container as they move in a straight line therebetween. The two vapor streams are generated at either sides of the conveyor, one upstream and the other somewhat downstream relative to the conveyor movement.
There are successful and widely used treating hoods which are provided with a system to prevent the impingement, to a great extent, of treatment vapor onto the finish of the containers being treated. This prevention of treatment on the finish has several beneficial results. Perhaps the most significant benefit is that it provides a container whose threaded finish will not be coated with a tin or titanium oxide coating. It has been found that threaded, metal halide coated necks of containers with closures applied frequently are difficult to remove by twisting of the closure from the threaded container.
Another problem that has been experienced is that with the use of tin as the surface treatment, there is a possibility that once a closure is applied, the tin treated surface and the closure may react, causing a rusting to occur. When the closure is applied to a full container, stored, and then later removed, the unsightly rust that may have formed makes the product less than appetizing to the consumer.
One of the most successful and most widely used types of treating apparatus is that designed by the American Glass Research and sold as the AGR-GCMI MARK II SnCL.sub.4 hot end applicator. This hood is provided with two pairs of blowers with one blower being used to propel the hot vapors across the conveyor and a second blower positioned vertically above the first to propel a stream of warm air across the finish portion of the container. Both the air stream and the lower, surface treating vapor producing flow are captured at the opposite side of the conveyor. In the case of the lower vapor flow, this is electrically heated and recirculated through a similar blower at the opposite side of the conveyor and directed back across the conveyor to treat the opposite surface of the container. Likewise, the air from the upper blower, which provides the air barrier across the finish of the container, is captured and vented through an exhaust system. A similar blower and air barrier is provided above the opposing vapor treating system. Thus, it can be seen that this particular arrangement provides an apparatus which has four blowers associated with each complete treatment hood. In addition to the blowers, each half of the hood is provided with electric heater elements in the recirculating duct and a thermostat for controlling the current to the elements. One problem experienced with these hoods has been the cleaning of the hoods and the maintenance of the hoods to prevent the burning-out of the blowers and the heater elements and the resultant loss of effective treatment during periods when the hoods are not efficiently operating or operating without the ware being treated.
When the AGR hood is in operation without all of the blowers working properly or without both heaters operating, the ware is not treated adequately nor is the unit operating with any degree of efficiency.